Downloaded and installed the February CU for SharePoint Server 2010 (KB 2597150), all went well, until running the config wizard and it failed!

So to the logs!!

psconfig log:

03/17/2012 13:53:50 8 ERR Task upgrade has failed with an unknown exception.
03/17/2012 13:53:50 8 ERR Exception:
Microsoft.SharePoint.Upgrade.SPUpgradeException:
Upgrade completed with errors. Review the upgrade log file located in [log Location].
The number of errors and warnings is listed at the end of the upgrade log file.
at Microsoft.SharePoint.Upgrade.SPUpgradeSession.CheckPoint()
at Microsoft.SharePoint.Upgrade.SPUpgradeSession.LogEnd()
at Microsoft.SharePoint.PostSetupConfiguration.UpgradeTask.Run()
at Microsoft.SharePoint.PostSetupConfiguration.TaskThread.ExecuteTask()

I know this is old, but I opened a ticket w/ MS for this, and they said it was safe to ignore the error.

Symptom:
Null Pointer error when running PSCONFIG following December 2010 cumulative update
Cause:
As per the Upgrade logs, following are our findings:

SPHierarchyManager when it is calling AddNextLevelObject which adds a specified object to the upgrade hierarchy as the child object of the specified object that is being upgraded.

The sequence when error is generated is during the process of web application getting upgraded.

But if we run through the log right after the error; SPHierarchyManager which calls Microsoft.SharePoint (in Microsoft.SharePoint.dll) and Microsoft.SharePoint.Upgrade.SPWssWebApplicationSequence.AddNextLevelObjects() is initiated and completed with the following entry in log:
at Microsoft.SharePoint.Upgrade.SPHierarchyManager.Grow(SPTree1 root, Boolean bRecursing, SPDelegateManager delegateManager)
at Microsoft.SharePoint.Upgrade.SPHierarchyManager.Grow(SPTree1 root, SPDelegateManager delegateManager)